1. Field of the Invention
The present invention relates to an ultrasonic transducer having a structure in which internal electrodes and piezoelectric elements are layered and an ultrasonic motor using the ultrasonic transducer.
2. Description of the Related Art
Ultrasonic motors have drawn attention in recent years as new motors which can be used in place of electromagnetic motors. The ultrasonic motors have the following advantages, compared with known electromagnetic motors.    (1) Low speed and high torque yielded without using gears    (2) High holding power    (3) Long stroke and high resolution    (4) Quiet    (5) No magnetic noise produced and no noise effects
Ultrasonic motors having such advantages include rotary motors, linear motors, and two-dimensional motors. An ultrasonic transducer is disclosed in U.S. Pat. No. 5,345,137 B1, which was filed by the applicant, as a known technology pertaining to the two-dimensional ultrasonic motors.
A known two-dimensional ultrasonic motor disclosed in U.S. Pat. No. 5,345,137 B1 will be described below with reference to FIGS. 13 to 15.
FIGS. 13 to 15 are diagrams illustrating the structure example of the known two-dimensional ultrasonic motor. FIG. 13 is a perspective view showing the structure of an ultrasonic transducer used in the two-dimensional ultrasonic motor. FIG. 14 is an exploded perspective view of a first layered product used in the ultrasonic transducer in FIG. 13, viewed from above. FIG. 15 is an exploded perspective view of a second layered product used in the ultrasonic transducer in FIG. 13, viewed from above.
The structure of the ultrasonic transducer will now be described.
Note that in FIG. 13, numeral 101 denotes piezoelectric element, numeral 105a denotes outer electrode for ground, numerals 105b and 105c denote outer electrode, and numeral 107 denotes lead wire. Also, in FIG. 14 and FIG. 15, numeral 101 denotes piezoelectric element, numeral 107 denotes lead wire, numeral 108 denotes internal electrode, numeral 111 denotes first layered product, and numeral 112 denotes second layered product.
The known two-dimensional ultrasonic motor uses an ultrasonic transducer 100 shown in FIG. 13. The ultrasonic transducer 100 has a layered product 106 including a first layered product 106a and a second layered product 106b joined in series.
The first layered product 106a and the second layered product 106b each have a structure in which internal electrodes and piezoelectric elements are alternately layered.
Specifically, in the first layered product 106a, as shown in FIG. 14, a full electrode, a piezoelectric element, an internal electrode that is divided in half in a first direction, a piezoelectric element, a full electrode, a piezoelectric element, an internal electrode that is divided in half in a direction orthogonal to the first direction, a piezoelectric element, . . . are layered in this order.
In the second layered product 106b, as shown in FIG. 15, a full electrode, a piezoelectric element, a full electrode, a piezoelectric element, . . . are layered in this order.
The operation of the ultrasonic transducer will now be described.
Applying alternating voltage to the first layered product 106a in the ultrasonic transducer 100 having the structure described above excites flexural resonance in the XZ plane or flexural resonance in the YZ plane, the flexural resonance having a fixed end at the bottom of the ultrasonic transducer 100. Applying alternating voltage to the second layered product 106b in the ultrasonic transducer 100 excites vibration of the ultrasonic transducer 100 in the Z direction.
As shown in FIG. 13, a projection support 103 is provided on the top face of the ultrasonic transducer 100. Combining the vibration generates elliptical vibration having an arbitrary plane of vibration including the Z axis. Accordingly, pressing a driven body (not shown) toward a projection 104 on the projection support 103 moves the driven body in an arbitrary direction in the XY plane.